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Wednesday, 25 March 2015

Tyrannosaurus and Triceratops - friends at last?

Tyrannosaurus and Triceratops, not locked in mortal combat. Something must be wrong. Cretaceous interspecies adoption concept, mimicking similar behaviours seen in modern mammals and birds, by Chidumebi Browne. Prints are available here.

Is there a more iconic palaeontological scene than Tyrannosaurus facing down Triceratops? The artistic association of these taxa has existed since at least 1906 when the very first, highly influential restoration of Tyrannosaurus (by Charles Knight, of course) pictured these animals alongside each other (Glut 2008). This idea flowed into aspects the first dinosaur movies - The Ghost of Slumber Mountain(1918) and The Lost World (1925) (unsurprisingly, given how much these films are indebted to Knight) - and, by 1928, the year Knight completed the famous Field Museum mural of Tyrannosaurus and Triceratops, their adversarial relationship was truly cemented. Book illustrations, TV shows and films have so perpetually shown encounters between these species that it's difficult to think of a new angle on this scene. At least, that's what I thought until being contacted by Chidumebi Browne, who asked me about working up a second Tyrannosaurus picture for him, this time co-starring Triceratops. Instead of combat however, he wondered about likelihood of a juvenile Triceratops being 'adopted' by the tyrant, as some animals make the headlines for doing so today (see below). Clearly I liked the idea enough to carry out the commission (I try to avoid things I feel are too unreasonable), but is this pure speculation, playing on gaps in our knowledge, or is there something credible to this idea? Could Triceratops and Tyrannosaurus, after more than a century of conflict, learn to be friends?

The literature on animal adoption is vast, with something like 270 species of mammal and bird known to adopt juveniles of their own species (via kidnapping, accidental inheritance or other means - Riedman 1982; Avital et al. 1998). Interspecific adoption is far rarer however, and most records pertain to animals housed in zoos or wildlife park. These adoptions can work both ways: juveniles can 'recruit' surrogate parents as readily as parents adopt surrogate offspring (for instance, the bond between Owen, a young hippo, and Mzee, a century-old giant Aldabran tortoise, seems to mostly reflect efforts of the hippo). There is relatively little documentation of interspecies adoption in wild animals, however. The example everyone knows is the Kenyan lioness Kamunyak, who has become something of a sensation for her habit of adopting young oryx. She adopted at least six calves before she was last sighted in 2004, defending them from others - including predators, humans seeking to intervene, and oyrx mothers - as if they were her own cubs. At least one species of monkey, as well as wading, raptorial and passerine birds have also adopted and reared the juveniles of other species (Izar et al. 2006; Literak and Mraz 2011; Oswald et al. 2013). Brood parasitism - the offloading of parental duties to other species - clearly exploits this behaviour (Riedman 1982), and famously occurs in cuckoos, certain ducks and geese, cowbirds, fish and bees.

The significance and evolutionary purpose of these interspecific relationships remains mysterious in many cases. Of course, the internet is awash with suggestions that these species have become 'friends', typically accompanied by heavily-edited video footage showing two different species at their squeeful snugglywugilinest. If they feature predators engaging in joyful play or nurturing behaviour with usual prey species, all the better. According to those sagest of human beings - internet commenters - these examples of natural harmony show us - spiteful, war-making human beings - to be the real animals. Truly, we are awful.

In the real world, the causes of these relationships are considerably less fluffy. The fact that most interspecies adoptions develop in captivity is not surprising, likely resulting from the close quarters contact between individuals and the deficient of conspecifics. Desires for parents, mates or group behaviours in some animals may be so strong in some species that they become blinded to the clear differences between themselves and the only other individuals they know. It's difficult to know whether these examples provide good models for interspecific adoption in natural circumstances.

Pictured: trouble in the neighbourhood.

The rarity of wild cases of interspecies adoption makes it hard to draw any firm conclusions about its adaptive significance, if it even has any (Izar et al. 2006). Although juvenile animals may receive some benefit from being adopted (especially if the alternative is not having parents at all), most biologists consider interspecific adoption a mistake - 'misdirected parenting' from confused adults. For some instances of bird adoption, this might reflect the similar appearance of chicks within certain lineages: adults simply can't tell them apart (Oswald et al. 2013). The circumstances surrounding some 'adoptions' are truly bizarre, where adoptees are ex-prey items which have become surrogate offspring. This has certainly happened with sea eagles where, having brought local buzzard chicks back to their own nest, presumably to eat, they started rearing them instead (Literak and Mraz 2011). It is assumed that the appearance of a raptor chick in their nest overrode any feeding impulses of these eagles, and they successfully reared several buzzards in this fashion (Literak and Mraz 2011). The idea that these parenting 'misfires' reflect recognition errors is supported by at least one instance where Caspian terns, rearing Ring-billed gulls, dropped their degree of parenting as juveniles outgrew resemblance to typical tern offspring (Oswald et al. 2013).

It is less easy to explain adoption across taxonomic and ecological boundaries so wide that even passing resemblance is unlikely. It must be said here that peer reviewed literature on these cases is hard to find, at least in my experience, so much of what is reported online is found in documentariesand newsstories - not the most ideal venues for discussing complex, unusual animal behaviour (this is not a sleight against the experts featured in such outlets, just that these things are highly-edited and narrative-hungry, which often leads to embellishment and distortion of facts). As an example of how highly selective these reports can be, some stories of lions 'adopting' prey animals result from 45 minutes of observation, receiving justified scepticism from biologists. 45 minutes of coexistence does not equal a clear case of adoption, especially in species renowned for toying with easily overpowered prey.

Where these cases carry more reliability - such as the widely verified case of Kamunyak and her oryx calves - behavioural factors remain unclear. It seems unlikely that a lioness would visually confuse an oryx calf was her own, except for the possibility that her eyesight was very poor. I see explanations that possible recent, traumatic loss of her (genetic) offspring as premature on the available evidence, most likely spurred on by a desire to project human values into a simplified narrative. The fact that Kamunyak ended up eating the starved carcass of one of her adoptees, and became a serial adoptee suggests her condition might be more complex and deeper-seated than a response to one recent event. Moreover, if cub death is the catalyst for this behaviour, would it not be more common in other lions? As far as I'm aware, cub death is a pretty frequent occurrence. It also strikes me that lots of medical conditions - head trauma, brain tumours, organ malfunction leading to hormone imbalances, even certain diseases - can drastically alter animal behaviour. As far as I'm aware, no assessment of Kamunyak's health was made before she disappeared. I wonder if an illness of some kind is a more parsimonious explanation of Kamunyak's condition than complex, psychological trauma.

Let's bring all this back to Chidumebi's concept: could extinct dinosaurs have engaged in inter-species adoption, especially species as different as Triceratops and Tyrannosaurus? We certainly know that modern animals can establish these weird relationships even between animals as different as large predators and tiny prey. We also know that dinosaurs are capable of inter-species adoption, because modern birds engage in this behaviour. On these analogies, a Tyrannosaurus adopting a Triceratops is not too far fetched. We might assume that their morphological distinctions are so great that the tyrant is not misidentifying the ceratopsid for offspring of its own, and thus must be a 'behaviourally abnormal' tyrannosaur: a Cretaceous Kamunyak, if you like. The background tyrants are meant to be behaviourally 'normal', and have sighted the Triceratops calf - I expect, as is reported for many of Kamunyak's adoptions, that the Triceratops infant would not last long.

So... is this the first picture of an obviously slightly unhinged tyrannosaur?

This exercise is hampered ultimately by a lack of knowledge about the parentage of fossil dinosaurs however, and particularly that of tyrannosaurs. Despite the relative wealth of knowledge on tyrant dinosaur palaeobiology (they are extremely well studied compared to other fossil groups), we still know very little, if anything, about tyrannosaur parental behaviour. Parenting is so varied among reptiles and birds that even phylogenetic brackets are of questionable use here. Strong parental instincts seem like a prerequisite for interspecific adoption, and the evidence is equivocal for such instincts in Tyrannosaurus. Until we know more about this, the likelihood of the scene above remains questionable. Of course, that doesn't mean the image composition is without merit: there are scenarios where predators and baby prey individuals coexist peacefully, such as when adult prey animals have run off and juveniles, being slower, have hidden instead. Indeed, such scenarios likely explain some hastily dubbed predator-prey 'adoptions' reported in the media. At least that provides a partial answer to our question, then: could Tyrannosaurus and baby Triceratops get along? Probably - at least until the former got hungry.

Considering that tyrannosaurs at least were superprecocial, adoption behaviour may a curiousity indeed.

When it comes to things like this, question about individuality and self-awareness clearly spring into mind. Maybe animals like Kamunyak are simply another example of psychological and mental aspecys previously-thought-to-be-unique-to-humans.

Not mentioned is the possible imprinting of the hatchling on the first adult it sees. And the (perhaps only human) mood experienced when meeting something irresistibly 'cute' like a baby Trike. Putting aside the odds against such a scene, nevertheless I see a heart-warming movie here. And the artwork is absolutely wonderful.

Well this is like a one on a million shoot on animal behavior, but definitely happend in the 230MY of dinosaur existence , but for sure some predators would just ignore potential preys because they aren't hungry, or don't want to bother engulling such small calory intake, and that would be possibly more common between carnivore dinosaurs... but maybe herbivores displayed a better disposition for adopting another herbivores especies, because proximity in habitat or conductual behavior.

Hello, Mark. I would just like to say that this and your Scavenging Styracosaurus article are my personal favorites of yours, and I have been working on an animated mini-series based on them and a few other inspirations.

I would also like to apologize for not asking for your permission ahead of time to use your T-Rex design in your illustration. My mistake haha

That being said, I already finished part 1, and if you have any interest to see it, I would love to hear your opinions on it. It's only a smidge over 2 minutes long, so hopefully it won't take up too much of your time. Here it is: https://www.youtube.com/watch?v=yo0JzVjxjhQ

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Who is this 'Mark Witton' chap?

Dr Mark Witton is a palaeontologist and palaeoartist, affiliated with the University of Portsmouth, UK. My technical research is focused on pterosaurs - Mesozoic flying reptiles - but my artwork has introduced me to a wide array of different fossil animals that are just as interesting. I work as a freelance author, consultant and artist: check out my work at MarkWitton.com, follow me on Twitter @MarkWitton, and browse my books here. Contact me at wittonprints[at]gmail.com. Due to volume of email I can't always reply to messages, but I do my best.